The present invention is related to that disclosed in (1) U.S. patent application Ser. No. 08/916,870, entitled xe2x80x9cSystems and Methods for Implementing a Dynamic Cache in a Supervisory Control System,xe2x80x9d and (2) U.S. patent application Ser. No. 08/916,871, entitled xe2x80x9cSystems and Methods for Generating and Distributing Alarm And Event Notifications,xe2x80x9d which applications are commonly assigned to the Assignee of the present invention and filed concurrently herewith. The disclosures of these related patent applications are incorporated herein by reference for all purposes as if fully set forth herein.
The present invention is directed, in general, to process control systems and, more specifically, to process control systems and methods of operating the same that use a publish/subscribe data distribution scheme.
A present day process facility (e.g., a manufacturing plant, a mineral or crude oil refinery, etc.) is typically managed using a distributed control system. A contemporary control system includes numerous modules that are tailored to monitor and/or control various processes of the facility. Conventional means link these modules together to produce the distributed nature of the control system. This affords increased performance and a capability to expand or reduce (scale) the control system to satisfy changing facility needs.
Process facility management providers, such as HONEYWELL, INC., develop process control systems that can be tailored to satisfy wide ranges of process requirements (e.g., global, local or otherwise) and facility types (e.g., manufacturing, refining, etc.). Such providers have two principle objectives. The first objective is to centralize control of as many processes as possible to improve an overall efficiency of the facility. The second objective is to support a common interface that communicates data among various modules controlling or monitoring the processes, and also with any such centralized controller or operator center.
Each process, or group of associated processes, has one or more input characteristics (e.g., flow, feed, power, etc.) and one or more output characteristics (e.g., temperature, pressure, etc.) associated with it. Model predictive control (xe2x80x9cMPCxe2x80x9d) techniques have been used to optimize certain processes as a function of such characteristics. One MPC technique uses algorithmic representations of certain processes to estimate characteristic values (represented as parameters, variables, etc.) associated with them that can be used to better control such processes. In recent years, physical, economic and other factors have been incorporated into control systems for these associated processes.
Examples of such techniques are described in U.S. Pat. No. 5,351,184 entitled xe2x80x9cMethod of Multivariable Predictive Control Utilizing Range Control;xe2x80x9d U.S. Pat. No. 5,561,599 entitled xe2x80x9cMethod of Incorporating Independent Feedforward Control in a Multivariable Predictive Controller;xe2x80x9d U.S. Pat. No. 5,572,420 entitled xe2x80x9cMethod of Optimal Controller Design of Multivariable Predictive Control Utilizing Range Control;xe2x80x9d and U.S. Pat. No. 5,574,638 entitled xe2x80x9cMethod of Optimal Scaling of Variables in a Multivariable Predictive Controller Utilizing Range Control,xe2x80x9d all of which are commonly owned along by the assignee of the present invention and incorporated herein by reference for all purposes (the foregoing issued patents and U.S. patent application Ser. No. 08/490,499, previously incorporated herein by reference, are collectively referred to hereafter as the xe2x80x9cHoneywell Patents and Applicationxe2x80x9d).
The distributed process control systems used to monitor and control a process are frequently linked by common communication pathways, such as by a LAN architecture or by a WAN architecture. When a requesting node needs a datum from a responding node, it issues a request for the datum across the network and the responding node then returns the datum back across the network. This request/respond cycle is repeated as frequently as the requesting node needs the current value of the datum. Inevitably, this leads to data distribution problems on the network as data traffic on the network nears the maximum bandwidth of the network and bottlenecks are created at heavily requested nodes. There is a need in the art for improved control systems capable of distributing large amounts of data between nodes of a network without exceeding the bandwidth of the network and without forming bottlenecks at heavily requested nodes. In particular, there is a need in the art for improved control systems capable of supplying the latest values of needed data to a large number of nodes with the minimum amount of bus traffic.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a data distribution, or delivery, scheme that efficiently utilizes network bandwidth and limits bottleneck formation; such a scheme, by definition, is robust, reliable, deterministic and flexible. As introduced hereinabove, a typical process facility includes many associated processes, various ones of which are associated with different stages of some overall process (e.g., natural resource refining, filtration, gas/oil separation, fabrication or other like process). The present invention introduces systems and methods that optimize distribution of information and improve a cooperation between various facility process controls, whether peer-to-peer, client and server, or otherwise.
In the attainment of this primary object, the present invention provides systems and methods for controlling associated processes within process facilities and, in particular, for distributing data among nodes of a real time process control system that controls the same. An exemplary real time process control system includes a plurality of sensors, controllable devices, and communication paths, as well as a computer system. The sensors and controllable devices are associated with various ones of the processes of the process facility, and the communication paths associate the sensors and controllable devices with the computer system. The computer system operates on data relating to the process facility, and distributes the data among the nodes thereof. The nodes are associated with one another by ones of the communication paths also.
An exemplary computer system includes subscriber nodes that desire data associated with certain of the processes and a publisher node. The publisher node monitors subscription lists associated with the subscriber nodes and, in response thereto, selectively communicates instances of the data to the subscriber nodes using ones of the communication paths. The communication paths have data traffic capacities and the computer system controls data distribution using the publisher node to efficiently utilize such data traffic capacities.
In an advantageous embodiment, the foregoing system uses a report by exception scheme, that is described in detail hereinbelow, within the above-described subscribe/publish methodology to further reduce the amount of data traffic on the communications paths to increase the quantity of data that can be subscribed for a given bandwidth. Subscription allows subscriber nodes to request multiple items via a subscription list associated with the publisher nodes, rather than constantly forming or issuing its requests, and without any knowledge of the distribution of the items among other nodes. The report by exception scheme further reduces bandwidth by communicating data from the publisher node to the subscriber nodes when data has changed.
In a preferred embodiment, the subscription lists are modifiable, enabling the publisher nodes, and the system overall, to adjust dynamically to the needs of the subscriber nodes. This is an important aspect of this embodiment because it does not rely upon or expect long term, statistically configured static publication models. Further, this embodiment supports subscription lists that include xe2x80x9csituational,xe2x80x9d implementation-based, application-dependent or other like non-datum-by-datum (non-FIP, Fieldbus Foundation, etc.) information.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.